Oxidation of oleic acid



Patented Oct. 30, 1951 OXIDATION OF OLEIC ACID Daniel Swern and Hogan B.Knight, Philadelphia, Pa., assignors to the United States of America asrepresented by the Secretary of Agriculture No Drawing.

Application July 29,1949,

Serial No. 107,625

4. Claims.

(Granted under the act of March 3, 1883, "as

amended April 30, 1928; 370 0. G. 757) This application is made underthe act of March 3, 1883, as amended by the act of April 30, 1928, andthe invention herein described, if patented in any country, may bemanufactured and used by or for the Government of the United States ofAmerica. for governmental purposes throughout the world without thepayment to us of any royalty thereon.

This invention relates to a process of oxidizing oleic acid to produce9,10-dihydroxystearic acid and aliphatic monobasic and dibasiccarboxylic acids having an average chain length of about nine carbonatoms in a simple and economical manner.

Oleic acid is a readily available material which on oxidative cleavageyields 9,10-dihydroxystearic acid and valuable monocarboxylic anddicarboxylic aliphatic acids containing about nine carbon atoms in themolecule such as pelargonic and azelaic acids, respectively. Suchmonobasic acids are useful, for instance, as intermediates in theproduction of artificial flavors, while the dibasic acids are valuableintermediates in the manufacture of plastics, synthetic fibers andlubricants. Both monobasic and dibasic acids containing about ninecarbon atoms are also useful as intermediates in the production ofplasticizers and in chemical syntheses.

According to the invention, oleic acid, dissolved in a lower saturatedaliphatic carboxylic acid containing a catalytic amount of a suitablemetal salt selected from the group consisting of the organic andinorganic salts of cobalt and manganese dissolved therein, is contactedwith a free oxygencontaining gas such as air and free oxygen, as forexample, by blowing the solution with a stream of the freeoxygen-containing gas, at a temperature ranging from about roomtemperature (25 C.) to the boiling point of the said lower saturatedaliphatic carboxylic acid, for a length of time sufiicient to causeoxidative cleavage of the oleic acid, thereby converting the oleic acidto oxidation products including 9,l-dihydroxystearic acid in admixturewith monocarboxylic and dicarboxylic aliphatic acids having an averagechain length of about nine carbon atoms, such as pelargonic and azelaicacids, respectively. These resultant reaction products are thenrecovered by any suitable procedure, for example, by removal of thesolvent medium by distillation and resolution of the distillationresidue into its components by conventional procedures.

Any lower saturated aliphatic carboxylic acid, of a concentrationadapted to dissolve oleic acid may be used as the solvent in ourprocess. Suitable acids include, for instance, such lower saturatedaliphatic monocarboxylic acids as formic, acetic, propionic and butyricacids. The use of acetic acid, however, is preferred in view of itsready availability and the superior results obtained therewith.Aliphatic anhydrides, such as acetic or propionic, are also satisfactorysolvents.

The proportions of oleic acid and solvent acid may be varied within widelimits although it is usually desirable to use about 1 to 2 parts, byweight, of solvent acid for 1 part of oleic acid, since within thisdilution range the viscosity of the solution is suiiiciently low topermit a fine dispersion of the oxygen-containing gas.

The catalysts adapted for use in the process are the salts of cobalt andmanganese, the most effective catalysts being the cobalt salts, whichare therefore preferred. Any organic or inorganic acid salt of thesemetals which is soluble to an appreciable extent in the reaction mixturemay be used; however, it is usually advantageou to use a salt of theacid employed as the solvent medium in the process. Although smalleramounts of the catalyst may be used, maximum yields of the desiredcleavage products are usually obtained on oxidation of solutionscontaining about 0.25 percent, by weight, of the metal, based on oleicacid. Larger proportions of the metal salt, for instance, in amountscorresponding to about 1.25 percent of the metal component, based onoleic acid, do not appreciably increase the yields of the cleavageproducts.

The oxidation may be conducted at ordinary room temperature or withapplication of heat up to the boiling temperature of the solvent medium.The preferred temperature range is approximately from about 50 to C.Thus, at about 25 C. the reaction proceeds relatively slowly, and theyields of cleavage products are relatively low. When the process isconducted at the boiling point of the solvent, the yields are usuallylower than those obtained at temperatures within the preferred range.Furthermore, when operating in the preferred temperature range, not onlyis a large part of the uncleaved portion of oleic acid converted to9,10-dihydroxystearic acid, which is a valuable by-product of theprocess, but also only a small proportion of the oleic acid originallyemployed is oxidized to polymeric products.

The following examples illustrate the invention:

Eramplel A solution consisting of 1200 g. oleic acid, 2400 ml. ofglacial acetic acid and 12.7 g. of cobalt acetate (0.25% Co, based onoleic acid) was blown with a stream of finely dispersed oxygen at 65 C.for 256 hours. The acetic acid was then recovered by distillation at apressure of about 50 mm., yielding a cherry red, viscous oil asaresidue. This was refluxed for four hours with an excess of 3 N aqueoussodium hydroxide, and the resulting soap solution was acidified with anexcess of dilute sulfuric acid and extracted with ether. The ethersolution was washed with water until acid free, and most of the solventwas removed y was then cooled to about C., and the precipitated9,10-dihydroxystearic acid was filtered 011 and washed with cold etherto remove soluble, colored impurities. The yield of9,10-dihydroxystearic acid, M. P. 124 to 128 C., was about to Thecombined ether solutions were then evaporated, and the residue wasconverted to methyl esters by refluxing it for six hours with a largeexcess of anhydrous methanol (2ml./g.) and catalytic quantities of 95%sulfuric acid. The acid was neutralized by the addition of solid sodiumbicarbonate, and the excess methanol was recovered by distillation. Theresidue was rendered anhydrous by adding benzene followed by azeotropicremoval of water. The benzene was evaporated, and the residual methylesters yielded, on vacuum distillation, a fraction boiling at about 70C./4 mm. to 160 C./04 mm. which consisted almost exclusively of cleavageproducts. (saponification number 414-433; calculated for a 50:50 mixtureof methyl pelargonate and dimethyl azelaate, 423.) The yield was about65%.

Example I I The oxidation procedure of Example I was conducted at theboiling point of acetic acid for 128 hours. A 10% yield of9,10-dihydroxystearic acid and a 45% yield of clevage products(saponification number 355) were recovered as described in Example I.

Example IV The oxidation procedure of Example I was conducted at 100 C.for 264 hours. No 9,10-dihydroxystearic acid was obtained, and a 65%yield of cleavage products (saponification number 483) were recovered asdescribed in Example I.

In the foregoing examples, the oxidation can distillation. Theconcentrated ether solution 4 also be effected by blowing acorresponding amount of air in lieu of oxygen through the solution.Similar results are obtained by analogous precedures using another loweraliphatic acid such as formic, propionic or butyric acid in place ofacetic acid, and equivalent amounts of other cobalt salts such as cobaltoleate, cobalt llnoleate, cobalt chloride and the like in place ofcobalt acetate. When a manganese salt is used as a catalyst in place ofa cobalt salt the reaction rate is decreased and the yields of thecleavage products and 9,10-dihydroxystearic acid are lower.

The process of this invention is applicable to other monounsaturated,long-chain aliphatic acids such as elaidic, palmitoleic, petroselinic,vaccenic, ricinoleic and the like, and their functional derivatives inwhich the double bond is unaffected.

We claim:

1. A process of producing 9,10-dihydroxystearic acid comprisingcontacting oleic acid, dissolved in about twice its weight of aceticacid containing an amount of cobalt acetate corresponding to at least0.25% of cobalt on the basis of the oleic acid, with a freeoxygen-containing gas at a temperature of about from 50 to C., therebyconverting the oleic acid to oxidation products containing9,10-dihydroxystearic acid in admixture with monocarboxylic anddicarboxylic aliphatic acids having an average chain length of aboutnine carbon atoms.

2. The process of claim 1 wherein the contacting is efiected by blowingthe oxygen-containing gas in a stream through the oleic acid solution.

3. The process of producing 9,10-dihydroxystearic acid by the method ofclaim 1 and isolating the formed 9,10-dihydroxystearic acid.

4. The process of producing a mixture of monocarboxylic and dicarboxylicacids having. an average chain length of about nine carbon atoms by themethod of claim 1 and esterifying the acids of the resulting mixture.

DANIEL SWERN. HOGAN B. KNIGHT.

REFERENCES 012? ED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS I, Number Name Date 2,292,950 Loder et a1 Aug. 11,1942 OTHER REFERENCES Long et al., Ind. and Eng. Chem., vol. 23 (July1931). page 790.

1. A PROCESS OF PRODUCING 9.10-DIHYDROXYSTEARIC ACID COMPRISINGCONTACTING OLEIC ACID, DISSOLVED IN ABOUT TWICE ITS WEIGHT OF ACETICACID CONTAINING AN AMOUNT OF COBALT ACETATE CORRESPONDING TO AT LEAST0.25% OF COBALT ON THE BASIS OF THE OLEIC ACID, WITH A FREEOXYGEN-CONTAINING GAS AT A TEMPERATURE OF ABOUT FROM 50* TO 100* C.THEREBY CONVERTING THE OLECI ACID TO OXIDATION PRODUCTS CONTAINING9,10-DIHYDROXYSYEARIC ACID IN ADMIXTURE WITH MONOCARBOXYLIC ANDDICARBOXYLIC ALIPHATIC ACIDS HAVING AN AVERAGE CHAIN LENGTH OF ABOUTNINE CARBON ATOMS.